Field of the Invention
The present invention relates to a magnetic recording element which enables precisely defined domains of magnetization to be obtained.
To record data, it is known to use magnetic recording elements which consist essentially of a carrier covered with a layer of magnetic material, which carrier may take various forms such as, for example, a drum, a tape or a disc. Data is recorded on a recording element of this kind by means of at least one magnetic recording head in the vicinity of which the recording element moves, the head generally being formed by an electromagnet. To record a series of data items on the recording element, the electromagnet is energized at intervals, the effect of which is to create a series of small magnetic domains on the recording element.
To ensure that the recording element is suitably magnetized, while at the same time using an electrical current of only relatively small intensity to energize the head, it has been proposed to magnetize the element by the so-called "transverse" method, i.e. in such a way that in each of the magnetic domains formed on the element, the magnetic induction is perpendicular to the surface of the element. A recording element capable of being magnetized in this way is described and illustrated in particular in U.S. patent application Ser. No. 854,682 now U.S. Pat. No. 4,138,702, of Jean Georges Magnenet, filed on Nov. 25, 1977, as a continuation of U.S. patent application Ser. No. 651,156, now abandoned. Both of said applications are assigned to the assignee of the present invention.
The recording element which is described in these patent applications has a carrier made of a material of high magnetic permeability, such as soft iron or steel, this carrier being coated with a layer of magnetic material. This recording element can then be magnetized transversely by means of a recording head having a magnetic core on which a winding is wound, the core being formed in such a way as to have a recording pole and a flux-closing pole whose cross-section is greater than that of the recording pole, both these poles being situated close to the surface of the magnetic layer. The magnetic core and the carrier thus form a closed magnetic circuit having two air gaps, and the magnetic induction is thus perpendicular to the surface of the magnetic layer which passes through these two air gaps. However, the fact that the cross-section of the recording pole is considerably smaller than that of the flux-closing pole means that the level of magnetic induction in the air gap of the recording pole is sufficiently high to cause the magnetic layer to become magnetized whereas, in the air gap of the flux-closing pole, the level of magnetic induction is insufficient to magnetize the layer or interfere with the data recorded previously.
With a recording element of this kind, it is difficult to ensure that the magnetic domains are sharply defined. This fact, which it has been possible to demonstrate in particular by observing the orientation taken up by ferrous particles applied to the magnetized domains of such a recording element, proves particularly troublesome in cases where the recording element is intended for use in a magnetic printing machine such, for example, as that which is described and illustrated in a French patent application which was filed on Mar. 22, 1976 and published as No. 2,305,654. In this case, because latent magnetic images which are formed on the surface of the recording element and which correspond to images of the characters which are to be printed do not normally have sharply defined outlines, the characters which are printed often appear blurred and are even sometimes difficult to read.